Progressive-burning smokeless powder



Patented Nov. 7, 193

rnoonnssrvn-nonnmo SMOKELESS rownnn Elton R. Allison, Wharton, N. .lL, assignor to Hercules Powder Company, Wilmington, lDeL, a corporation of Delaware No Drawing. Application October 15, 1938, Serial No. 235,242

3 Claims.

This invention relates to a progressive-burning smokeless powder.

In order to make it possible to control closely the burning rate of smokeless powder and pro- 5 duce a high velocity of the projectile without high breech pressures, it has been customary to coat the grains of the smokeless powder with a deterrent material explosive or non-explosive which will retard the initial burning rate of the powder grains. Such coating material, however, penetrates. the powder grains more or less so that as the powder burns, the successively exposed surfaces contain gradually less and less of the deterrent material, thus causing the combustion of the grains to proceed with increasing speed.

Treatment of smokeless powder grains to render their combustion progressive by applying thereto a deterrent by methods heretofore known, while producing the desired results to a degree,

has been open to a number of objections. The deterrents heretofore used have been more or less good solvents for the nitrocellulose of the smokeless powder, and consequently, even if applied on the surface of the powder grain, have penetrated to a depth into the powder grain depending upon the conditions of treatment, e. g., a longer time of heating of the powder grains with the deterrent or solution of the deterrent causing a deeper penetration of the deterrent into 0 the powder grains than would otherwise be the case.

Powder grains treated with a deterrent which is a solvent for the nitrocellulose of the powder grains tend to penetrate more and more deeply into the powder grains during storage of such progressive-burning smokeless powder, particularly during storage of said powder during hot periods of the year or in hot climates. As a result, the concentration of the deterrent on the surface of the powder grain becomesless and less with the age of the powder grains, and the deterrent action on the surface of the powder grain consequently becomes less and less on storage. The result thereof is that powder grains deterred by a deterrent which is a solvent of the nitrocellulose in the powder grain, do not remain ballistically stable, i. e., the ballistics of the powder change with the age of the powder due to the disappearance of the deterrent from the surface of the powder grain.

In the preparation of coated smokeless powder in accordance with my invention, I use as the coating agent petroleum hydrocarbon-insoluble resin derived from pine wood. This resin is not a solvent for the smokeless powder grains, but

because of its resinous nature it adheres strongly to the powder grain and because of its high melting point it leaves a hard, non-tacky surface on the grain. It is not believed that the resin used in accordance with my invention penetrates into 5 the grain except as it is carried into the grain mechanically by the solvents used in applying it. In any case, however, penetration is very slight and it either does not continue on storage, or if it does, it progresses so slowly as to have no ef- 10 fects on the ballistics of the powder.

The resin which I use as a coating agent and designate herein as petroleum hydrocarbon-insoluble resin derived from pine wood may be prepared by extracting pine wood with a coal .15 tar hydrocarbon, such as benzol or toluol, then evaporating the volatile constituents, leaving a residue consisting of a mixture of wood rosin and theresin used in the present invention. Extraction of this mixture with a petroleum hydrocar- 20 icon such as, for example, gasoline, dissolves the rosin and after separation of the rosin, high in abietic acid, there remains a resinous residue low in abietic acid. This resin is characterized by substantial insolubility in cold petroleum hydro- 5 carbons, but will differ somewhat in its specific characteristics such as acid number, melting point, exact petroleum ether solubility and content of naphtha and toluol soluble matter, depending upon the method for the recovery of ,30 rosin from pine wood used in its production. This resin is more fully described and claimed in the co-pending application, Serial No. 61,745, filed on January 1, 1936, by Lucius C. Hall.

I may apply petroleum hydrocarbon-insoluble 35 resin derived from pine wood to the smokeless powder grains in solution in a solvent which is substantially a non-solvent for the smokeless powder grains or in a solvent or mixed solvents having a mild solvent action on the smokeless ,40 powder grains or I may apply the resin dissolved in a suitable solvent the form of an aqueous emulsion. As solvents having appreciably no action on the smokeless powder grains I may use for example ethyl alcohol, propyl alcohol, iso- 45 propyl alcohol, benzol and the like, or I may use a mild solvent such as, for example, ethyl alcohol with'a minor amount of an alkyl acetate, for example, ethyl or butyl acetate.

, The coating operation may be carried out in ,50 any suitable apparatus such as, for example, a sweetie barrel. The smokeless powder grains may be treatedat temperatures varying between about 110 C. and about C., and the time of treatment may vary depending upon the composition 55 of the powder and the size of the powder grains treated. The amount of deterrent applied is also variable, depending upon the deterrent characteristics desired in the final powder, but in general, it will vary from about 0.5 part to about parts by weight of my deterrent per 100 parts by weight of the powder grains being treated.

While both single base and double base powders may be coated with my deterrent in accordance with my invention, I have found that my deterrent is particularly effective with double base smokeless powder.

After the powders have been coated as indicated above they are removed to a dry house, and after drying for a suiiicient length of time may be glazed with graphite, screened, and loaded into cartridges in the manner well known to the art.

Having described my invention in a general manner I will now proceed to a more detailed description thereof by reference to the following examples.

Example 1 A collcided smokeless powder containing 40% nitroglycerine was extruded through a 0.045 inch die containing a 0.015 inch pin and the strands so produced cut into 21 particles per inch. Nine hundred and eight parts by weight of these powder grains were coated with 18.1 parts by weight of these powder grains were coated with 18.1 parts by weight of petroleum hydrocarbon-insoluble resin derived from pine wood, dissolved in 80 parts by weight of ethyl alcohol. These powder grains were tumbled in a sweetie barrel with the deterrent solution for hour at 75" C. The powder was then removed and dried for'two days at 55 0., glazed with graphite, screened, and brought to the proper moisture content. Sixteen and twotenths grains of this powder when fired in a .410 gauge shot shell with ounce of No. 9 shot, gave a velocity of 880 feet per second over a '35 foot range and a breech pressure of 12,600 pounds per square inch.

In comparison with the above, 908 parts by weight of the same powder were coated with 18.1 parts by weight of diethyldiphenyl-urea dissolved in 80 parts by weight ethyl alcohol. These powder grains were tumbled with the deterrent solution in the sweetie barrel for hour at 75 C., and finished as above. Seventeen and two-tenths grains of this powder when fired in the .410 gauge shot shell with ounce of No. 9 shot gave a velocity of 883 feet per second over a 75 foot range, and a breech pressure of 14,800 pounds per square inch. It will be noted that the breech pressure produced in the case of the solvent coated powder is 2,200 pounds per square inch higher than when coated with my deterrent.

Example 2 A collcided smokeless powder containing nitroglycerine was extruded through a 0.065 inch die containing a 0.020 inch'pin and the strands so produced cut into 325 particles per inch. Fifty parts by weight of these flake powder grains were coated with 1.75 parts by weight of petroleum hydrocarbon-insoluble resin derived from pine wood dissolved in 4.5 parts by weight of hot ethyl alcohol. The powder and coating solution were tumbled together in a sweetie barrel for /2 hour at room temperature. The powder was then removed, dried for 2 days at 55 C., glazed, screened, and brought to the proper moisture con tent. Thirty-six grains of a blend of 18 parts by weight of this powder and 2 parts by weight of the same powder uncoated were loaded in a 12 gauge shot shell with 1 ounces of No. 6 shot. When fired, this powder gave a velocity of 1002 feet per second over a 120 foot range and a breech pressure of 11,500 pounds per square inch.

After days storage at C. this same charge of powder gave a velocity of 1003 feet per second and a breech pressure of 11,900 pounds per square inch.

As a comparison with this powder, I coated 200 parts of the same base powder with 9 parts by weight of diethyl phthalate, dissolved in ethyl alcohol in the same manner as above, followed by the same treatment as shown before. Thirtyeight and five-tenths grains of this powder loaded in the same shells when fired gave a velocity of 999'feet per second over the same range with a breech pressure of 10,300 pounds per square inch. After 13 days storage at 0., this powder when fired in the same manner gave a velocity of 998 feet per second and a breech pressure of 12,200 pounds per square inch.

It will be noted that even after 13 days storage, powder coated with the solvent deterrent gave an increase in breech pressuer of practically 2000 pounds per square inch, whereas the powder coated with my deterrent after 30 days storage at practically the same temperature showed a pressure increase of only 400 pounds per square inch. The superior storage stability of powder coated with my deterrent is thus clearly indicated.

Example 3 A collcided smokeless powder containing 20% nitroglycerine was extruded through a 0.065 inch die containing a 0.020 inch pin and the strand so produced cut into 200 particles per inch. Fifty parts by weight of these flaked powder grains were coated with 1 part of petroleum hydrocarbon-insoluble resin derived from pine wood. dissolved in 3 parts by weight of ethyl alcohol in the same manner as indicated in Example 2. The powder grains were also finished as indicated in Example 2. lfhirty-five and five-tenths grains of this powder in a 12 gauge shot shell using 1%; ounces of No. 6 shot gave a normal velocity of 906 feet per second over a 120 foot range and a breech pressure of 10,600 pounds per square inch. After 30 days storage at 50 C. this powder when fired in a similar manner gave a velocity of 990 feet per second, and a breech pressure of 10,600 pounds per square inch. The excellent storage stability of my deterrent coated powder is again very clearly indicated.

It will be understood that the details and examples hereinbefore set forth are illustrative only and that the invention as herein broadly described and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. Smokeless powder surface coated with petroleum hydrocarbon-insoluble resin derived from pine wood, characterized by being progressive-.

burning.

2. Double base smokeless powder surface coated with petroleum hydrocarbon-insoluble resin derived from pine wood, characterized by being progressive burning.

3. Smokeless powder, surface coated with petroleum hydrocarbon-insoluble resin derived from pin wood in amount from about .5% to about 10% by weight of the powder, characterized by being progressive-burning.

ELTON R. ALLISON. 

